Electron discharge device



Sept. 15, 1936. A I D ONEILL 2,054,229

ELECTRON DISCHARGE DEVICE Filed April 26, 1935 24 06 .0704; lNVEN-r'oR F AHQBNEY Patented Sept. 15, 1936 UNITED STATES PATENT OFFICE ELECTRON DISCHARGE DEVICE Application April 26, 1935, Serial No. 18,353

9 Claims.

This invention relates to electron-discharge devices and more particularly to wave repeating or amplifying devices such as radio tubes or the like.

In certain types of radio tubes, particularly those which are used as voltage amplifiers, the dynamic plate-resistance is a very important factor and should preferably be maintained as high aspossible for different values of plate voltage. In the case of those tubes having a shield around the plate, it has been found that with the usual type of construction when the anode voltage approaches the shield voltage, the dynamic plate resistance, due to the lowered plate-shield potential gradient, is materially lower than when the anode is at a substantially higher Voltage than the shield. Consequently under these conditions, any change in plate current whether resulting from a change of primary or secondary electron flow to or from the plate, ap-

. pears as a change in the dynamic plate resistance of the tube. When the potential gradient between the shield and plate is lowered, any small change in the plate voltage will produce an abnormally large variation in the plate current, which is equivalent to a lowered dynamic plate resistance.

Accordingly, one of the principal objects of this invention is to provide an arrangement for controlling the dynamic plate resistance of electron 3g discharge tubes especially, although not necessarily, so-called voltage amplifier tubes.

A feature of the invention relates to a tube of the screened anode type, having means for minimizing the controlling influence of the alternating plate voltage upon electrons moving radially from the cathode or screen grid toward the edge of the plate.

Another feature relates to a tube of the screened-plate type wherein means are provided to control the secondary emission from the plate to the shield or from the shield to the plate in such a way as to increase the apparent dynamic plate resistance of the tube.

A further feature relates to a screened-plate radio tube having a specially designed shield whereby the screen and plate may be operated with relatively low voltage gradient therebetween, without correspondingly reducing the dynamic plate resistance of the tube.

A still further feature relates to the novel organization, arrangement and relative location of parts which go to make up an improved electron discharge repeater or amplifier of the screened-plate type.

e Other features and advantages of the invention not specifically enumerated will be apparent after a consideration of the following detailed description and the appended claims.

While the invention will be described herein as embodied in one particular type of tube, it will be understood that this is done merely for purposes of explaining the invention and not by way of limitation. Accordingly in the drawing,

Fig. l is a partial vertical sectional view of the upper portion of a tube mount embodying the invention.

Fig. 2 is a sectional view of the tube mount of Fig. 1 taken along the line 22 thereof.

Fig. 3 is a schematic diagram to explainthe invention.

Referring to Figs. 1 and 2, the numeral l indicates any wellknown form of electron-emitting cathode comprising for example a tubular metal sleeve 2 on the exterior of which is an electronemissive coating 3. Insulatingly mounted within the sleeve 2 is a heater filament 4 of any wellknown construction. It will be understood of course that any other type of emitting cathode, such for example as a filamentary cathode, may be employed. Surrounding the cathode is a foraminous control grid 5 which may be formed with a pair of side rods or uprights 6, 1, around which is helically wound the grid wire 8. Surrounding the control grid 5 is another similar grid 9 consisting of a pair of side rods or uprights In, H, around which is helically wound the grid wire l3. Likewise a third grid l4 surrounds grid 9, grid I4 beingformed with a pair of side rods l5, [6, around which is helically wound the grid wire 11. It will be understood that the various side rods or grid supports are fastened to, or otherwise supported in a suitable standard such as the usual reentrant' press (not shown) in the manner for example as shown in Patent No. 1,950,456. Surrounding the cathod and grids is a tubular metal plate l8 which is fastened to a pair of side rods or supports I9, 20. Surrounding the plate i8 is a screen consisting of a wire mesh cage 2! having fastened to its upper edge a metal cap member 22. The cap member 22 is provided with a transverse slot through which pass the several side rods 6, I, I0, ll, [5, E6, the slot having a transverse width greater than the diameter of the largest side rod so as to prevent short-circuiting of the various grids. The plate l8 and the mesh cage 21 may be supported at their lower ends from the tube press in a manner similar to that in which the remaining electrodes are supported.

For the purpose of spacingthe electrodes accuratelyfrom each other, and for preventing contact of the grid side rods with the edges of the slot in cap 22, there is provided an insulator disc 23 of mica or other suitable material having a series of aligned perforations to receive the cathode sleeve 2 and the various side rods described above. A similar mica disc may be positioned at the lower end of the mount to space the are inserted in the top cap member 22 the edges of the springs 28 and 29 being adapted toengage flexibily the inner wall of the enclosing envelope the plate or anode l8.

plate reaching the screen-grid 9.

in the manner described in detail in application Serial No. 700,638, filed December 2, 1933. Suitable lead in wires are provided for the various electrodes and preferably the lead-in wire St] for the control grid 5 is taken out through the top of the tube.

With the .above, construction, it' will be noted that since the outer screen including the members 2| and 22 substantially completely encloses the plate 88, it is necessary that the said plate 88 be shorter than the outer screen 2 'When the tube above described is used in the usual way as a pentode the input signals are impressed in any wellknown manner across the cathode 3 and the control grid 5. The grid 9 which may function as a shield grid has a suitable constant positive potential impressed thereon which potential is preferably lower than the potential impressed upon The grid' l4 may function as the so-called suppressor grid and may be connected to the'cathode 3 or may be maintained in any. other manner at or near the cathode potential. With this arrangement, the primary electrons that'are ,emittedfrom the cathode 3 travel through the successive grids 5, 9 and I4 until they reach the plate or anode 8. When these primary electrons strike the screen-grid 9 secondary electrons may be. released from the screen and likewise when the primary electrons strike the plate I8 other secondary electrons may be released from the said plate. If the potential gradient between the screen-grid 9 and the plate I8 is sufiiciently high, the majority of these secondary electrons will be attracted toward the plate H? which is more positive than the screen 9. In accordance with its usual function the suppressor grid I4 tends to preventthe secondary electrons from the Where the potential gradient between the plate electrode l3 and the outer screen 2| is relatively low an appreciable number of electrons, particularly those electrons that are moving in a straight line to the edge of the plate, may have sufficient velocity to pass over the upper edge of the plate I8 tothe outer shield 2|. Consequently a slight change in the plate voltage by changing the potential gradient between the plate and shield will cause a disproportionate change in the number of electrons which avoid the plate l8 and reach the shield 2 9.

Furthermore the electrons which are released from the screen 13 and which are moving radially toward the edge of the plate I8 may with one potential gradient between the plate and shield reach the plate while withanother potential gra client the same electrons may pass by the edge of the plate and eventually reach the shield 2|. In order to overcome this condition there is mounted adjacent the edge of the plate l8 and preferably plate i8 as indicated schematically in Fig. 3 of the drawing.

The insulator disc 3| has a two-fold purpose: it prevents the escape of secondary electrons from the edge of the plate to the outer screen 2| or the shield 22, and it serves to prevent the attraction to the plate |8 of electrons passing above the disc 3i or the escape over the edge of the plate of electrons passing under the disc. In like manner the disc 33, if used, serves to restrict to the plate, electrons passing above the disc and to prevent those electrons passing below the disc from reaching the plate, and prevents the escape of secondary electrons from the plate [8 to the outer shield 2|. It should be emphasized that both the attraction of electrons and emission of secondary electrons are to be understood as the variation in these effects due to the alternating component of plate voltage. It has been found that by using the member 3| the undesirable effects described are so minimized that, where the plate voltage is reduced to approximately that of the voltage on the screen 2|, a substantial increase in the dynamic plate resistance of V the tube is obtained. For instance with the plate I8 and the screen 13 at volts positive with respect to the cathode, a five-fold increase in plate resistance was obtained over that obtainable without the member 3|.

While one specific embodiment of the invention is disclosed herein it will be understood that various changes and modifications may be made -herein without departing from the spirit and scope of. the invention. Thus while the drawing shows member 3| extending in a plane substantially perpendicular to the longitudinal axis of the mount if desired member 3| may be in the form of a cylindrical collar mounted to form an extension of the plate l8 it being understood that the edge of the insulating collar will preferably be in close contact with the edge of the plate.

What I claim is: g

1. In an electron-discharge tube, an electronemitting cath0de, a plate electrode, a control grid and a shield grid between said cathode andplate electrode, said shield grid extending beyond the end of the plate electrode, an external screen for said plate electrode, and'an insulator shield adjacent an edge of the plate electrode and extending only part way into the space between the plate electrode and shield grid to reduce substantially the edge effect of said plateelectrode upon the dynamic plate resistance of the tube.

2. In an electron-discharge tube, an electron and an annular insulator member mounted around the edge of the plate and extending only part way into the space between the plate and the inner shield member.

3. A mount for a tube of the pentode type having inner and outer shielding electrode members for the plate electrode and extending beyond the end thereof, an annular insulator shield mounted adjacent one edge of the plate electrode and extending only part way into the space between the plate electrode and the suppressor grid, said insulator serving to reduce the edge effect of the plate electrode on electrons moving past the edge of said plate electrode.

4. A pentode mount according to claim 3 in which the plate electrode of the pentode is foreshortened with respect to the outer shield electrode member and the annular insulator member is in contact with the edge of the plate electrode.

5. In an electron-discharge tube, an electronemitting cathode, a plate electrode, a plurality of grid electrodes between the cathode and plate electrode, an insulator disc for spacing said cathode and grid electrodes from each other, and another insulator disc mounted adjacent the edge of. the plate electrode and through which said grid electrodes extend, said other insulator serving to reduce the edge effect of said plate on electrons moving past the edge of said plate.

6. In an electron-discharge tube, an electronemitting cathode, a control grid, a shield grid, a plate electrode, said shield grid extending beyond the end of said plate electrode and an annular ring of insulation in contact with the edge of the plate electrode and extending only part way from said plate electrode toward said shield grid to reduce the edge effect of said plate electrode on electrons moving past the edge of said plate.

7. An electron-discharge tube according to claim 6 in which an outer shield surrounds the plate electrode and extends beyond the ends of said plate electrode.

8. In an electron-discharge tube, an electronemitting cathode, a plate electrode, a cup-shaped member enclosing said plate electrode and in spaced relation to the edge thereof, a shield grid electrode extending beyond the edge of said plate providing a clear path for the passage of electrons past the edge of said plate to said screen electrode, and a ring of insulation in contact with the edge of the plate electrode to reduce the edge effect of said plate electrode on said electrons.

9. In an electron-discharge tube, an electronemitting cathode, a plate electrode surrounding said cathode, a shield electrode surrounding said plate'electrode, said plate electrode being foreshortened with respect to said shield electrode, and insulator rings one in contact with each edge of the plate electrode to reduce the edge effect of. said plate electrode on electrons moving past the edges of said plate electrode.

GEORGE DEAN ONEILL. 

